U.S. patent application number 12/297427 was filed with the patent office on 2009-12-17 for image-pickup device and display apparatus.
This patent application is currently assigned to Sony Corporation. Invention is credited to Masafumi Matsui, Yoshiharu Nakajima, Yasuyuki Teranishi.
Application Number | 20090310007 12/297427 |
Document ID | / |
Family ID | 39709927 |
Filed Date | 2009-12-17 |
United States Patent
Application |
20090310007 |
Kind Code |
A1 |
Matsui; Masafumi ; et
al. |
December 17, 2009 |
IMAGE-PICKUP DEVICE AND DISPLAY APPARATUS
Abstract
An image-pickup device includes a photoelectric conversion
element 5 that converts light into electric charge, a capacitor 6
that stores electric charge which the photoelectric conversion
element 5 has obtained by conversion, reset means 7 for discharging
the electric charge in the capacitor 6, and an amplifying thin-film
transistor 8 that receives, amplifies, and outputs the electric
charge stored in the capacitor 6. In addition, the image-pickup
device is configured so that the amplifying thin-film transistor 8
forms a source follower circuit.
Inventors: |
Matsui; Masafumi; (Kanagawa,
JP) ; Nakajima; Yoshiharu; (Kanagawa, JP) ;
Teranishi; Yasuyuki; (Kanagawa, JP) |
Correspondence
Address: |
ROBERT J. DEPKE;LEWIS T. STEADMAN
ROCKEY, DEPKE & LYONS, LLC, SUITE 5450 SEARS TOWER
CHICAGO
IL
60606-6306
US
|
Assignee: |
Sony Corporation
Minato-ku Tokyo
JP
|
Family ID: |
39709927 |
Appl. No.: |
12/297427 |
Filed: |
February 7, 2008 |
PCT Filed: |
February 7, 2008 |
PCT NO: |
PCT/JP2008/052056 |
371 Date: |
February 26, 2009 |
Current U.S.
Class: |
348/311 ; 345/92;
348/333.01; 348/E5.022; 348/E5.091 |
Current CPC
Class: |
G09G 3/3648 20130101;
G09G 2300/0465 20130101; G02F 1/13338 20130101; G06F 3/0412
20130101; G06F 3/042 20130101; G02F 1/13312 20210101 |
Class at
Publication: |
348/311 ; 345/92;
348/E05.091; 348/333.01; 348/E05.022 |
International
Class: |
H04N 5/335 20060101
H04N005/335; G09G 3/36 20060101 G09G003/36 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2007 |
JP |
2007 040148 |
Claims
1. An image-pickup device characterized by comprising: a
photoelectric conversion element that converts light into electric
charge, a storage capacitor that stores the electric charge which
the photoelectric conversion element has obtained by conversion,
reset means for discharging the electric charge in the storage
capacitor, and an amplifying thin-film transistor that receives,
amplifies, and outputs the electric charge stored in the storage
capacitor, and characterized in that a source electrode of the
amplifying thin-film transistor is connected to a power-source
supplying line, a gate electrode of the amplifying thin-film
transistor is connected to the storage capacitor, and the
amplifying thin-film transistor forms a source follower
circuit.
2. The image-pickup device according to claim 1, characterized in
that the photoelectric conversion element comprises a sensor
thin-film transistor in which a leakage current changes in
accordance with an amount of received light.
3. The image-pickup device according to claim 2, characterized in
that the reset means comprises a reset thin-film transistor that is
disposed between the storage capacitor and a ground wire.
4. The image-pickup device according to claim 2, characterized in
that the reset means comprises a reset function which the sensor
thin-film transistor has, and a function of switching a gate
voltage that is to be applied to the sensor thin-film transistor,
and in that the reset means is configured, for the sensor thin-film
transistor that functions as the photoelectric conversion element
when the gate voltage is lower than a threshold, in such a manner
that the switching function switches the gate voltage so that the
gate voltage is set to be equal to or higher than the threshold,
whereby the electric charge in the storage capacitor is discharged
by the reset function.
5. A display apparatus characterized by comprising: image display
elements that are disposed in a matrix, and image-pickup devices
that are attached to the image display elements, the image-pickup
devices including photoelectric conversion elements that convert
light into electric charge, storage capacitors that store the
electric charge which the photoelectric conversion elements have
obtained by conversion, reset means for discharging the electric
charge in the storage capacitors, and amplifying thin-film
transistors that receive, amplify, and output the electric charge
stored in the storage capacitors, characterized in that source
electrodes of the amplifying thin-film transistors are connected to
a power-source supplying line, gate electrodes of the amplifying
thin-film transistors are connected to the storage capacitors, and
the amplifying thin-film transistors form source follower circuits,
and characterized in that at least the photoelectric conversion
elements, the storage capacitors, and the amplifying thin-film
transistors are integrated, and disposed in correspondence with the
image display elements.
6. The display apparatus according to claim 5, characterized by
being configured so as to read, in a field period, stored electric
charge in the storage capacitors after discharging of electric
charge is performed by the reset means, so as to read, in the next
field period, stored electric charge in the storage capacitors in a
state in which discharging of electric charge is not performed by
the reset means, and so as to determine amounts of electric charge
that are converted by the photoelectric conversion elements from
differences between respective read results.
7. The display apparatus according to claim 5, characterized by
being configured, when the photoelectric conversion elements, the
storage capacitors, and the amplifying thin-film transistors are
also disposed in the matrix in correspondence with the image
display elements, so as to perform, in a field period, reading of
stored electric charge in the storage capacitors of even rows of
the matrix, and so as to perform, in the next field period, reading
of stored electric charge in the storage capacitors of odd rows of
the matrix.
8. The display apparatus according to claim 5, characterized by
being configured, when the photoelectric conversion elements, the
storage capacitors, and the amplifying thin-film transistors are
also disposed in the matrix in correspondence with the image
display elements, so as to perform, in one field period, based on
common signals, both reading of stored electric charge in the
storage capacitors of rows of the matrix, and discharging of
electric charge by the reset means for the storage capacitors of
rows which are each disposed one row prior to the corresponding row
in a reading sequence.
9. The display apparatus according to claim 5, characterized by
being configured so as to perform, in the same clock cycle in one
field period, both reading of stored electric charge in the storage
capacitors, and discharging of electric charge by the reset means
for the storage capacitors.
Description
TECHNICAL FIELD
[0001] The present invention relates to an image-pickup device
including photoelectric conversion elements, and a display
apparatus.
BACKGROUND ART
[0002] While, in general, photoelectric conversion elements, such
as CCD (Charge Coupled Devices) sensors and CMOS (Complementary
Metal Oxide Semiconductor) sensors, have been known as image-pickup
devices that pick up images, recently, it has been proposed that
thin-film transistors (hereinafter, "Thin Film Transistor" is
abbreviated as "TFT") are caused to function as photoelectric
conversion elements in combination with capacitors or the like. As
one example of such image-pickup devices, for example, there are
image-pickup devices that include liquid-crystal display elements,
TFTs that function as photoelectric conversion elements, and so
forth for respective pixels disposed in a matrix, and that also
include a backlight or frontlight which serves as a light source.
The image-pickup devices are configured so as to be capable of
performing information input by utilizing light incident onto the
TFTs while the image-pickup devices perform image display by
utilizing transmission of light from the light source through the
liquid-crystal display elements (for example, see Patent Document
1). Because the image display and the information input can be
performed in the same display region in the above-mentioned
configuration, it is expected that the image-pickup devices are
used as information input/output devices as replacements for touch
panels.
[0003] When the above-described image-pickup devices of a
display-function-integrated type are realized using a commonly
known low-temperature polysilicon technique, it is considered that
it is difficult to obtain accurate output values because it is
impossible to disregard attenuation of signals that is caused by
parasitic capacitances in panels. The reason is that a
photocurrent, which occurs due to light irradiation, in the case of
a low-temperature polysilicon (hereinafter, abbreviated as "p-Si")
is smaller than that in the case of an amorphous silicon
(hereinafter, abbreviated as "a-Si"). Thus, in order to realize the
image-pickup devices of a display-function-integrated type using
the p-Si, a certain amplification function is necessary. As a
specific example of such an amplification function, there is an
amplification function of storing electric charge in capacitances,
such as capacitors, in accordance with electric signals that are
generated in the photoelectric conversion elements, converting the
electric charge into voltages, storing the converted voltages in
SRAMs (Static Random Access Memory), and outputting the voltages as
digital values "1" or "0" (for example, see Patent Documents 2 and
3). According to the amplification function, because the SRAMs have
also the amplification function, no attenuation of signals that is
caused by parasitic capacitances in panels occurs. Furthermore,
because the voltages are output as the digital values, output
results of the voltages have an excellent noise tolerance. [0004]
Patent Document 1: Japanese Unexamined Patent Application
Publication No. 2002-268615 [0005] Patent Document 2: Japanese
Unexamined Patent Application Publication No. 2001-292276 [0006]
Patent Document 3: Japanese Unexamined Patent Application
Publication No. 2001-339640
DISCLOSURE OF INVENTION
Technical Problem
[0007] However, in the above-described prior art, the outputs after
the amplification function is performed are the digital values of
"1" or "0", i.e., binary values. Thus, it is very difficult to
excellently represent half tones for image-pickup results, and a
complicated process or operation, such as setting of a plurality of
image-pickup conditions, is necessary in order to represent the
half tones.
[0008] Therefore, it is an object of the present invention to
provide an image-pickup device and a display apparatus that can
perform analog output which allows half tones to be excellently
represented, for example, even when the image-pickup device of a
display-function-integrated type is configured using a p-Si.
Technical Solution
[0009] The present invention provides an image-pickup device that
has been invented in order to achieve the above-described object.
The image-pickup device is characterized by comprising a
photoelectric conversion element that converts light into electric
charge, a storage capacitor that stores the electric charge which
the photoelectric conversion element has obtained by conversion,
reset means for discharging the electric charge in the storage
capacitor, and an amplifying thin-film transistor that receives,
amplifies, and outputs the electric charge stored in the storage
capacitor. A source electrode of the amplifying thin-film
transistor is connected to a power-source supplying line, a gate
electrode of the amplifying thin-film transistor is connected to
the storage capacitor, and the amplifying thin-film transistor
forms a source follower circuit.
[0010] In the image-pickup device configured as described above,
since the amplifying thin-film transistor forms the source follower
circuit, when the amplifying thin-film transistor amplifies and
outputs the electric charge stored in the storage capacitor, analog
output can be performed by utilizing the source follower circuit.
Thus, for example, even when the photoelectric conversion element
is a sensor thin-film transistor in order to be easily integrated
with a display function, analog output can be performed as in the
case of a CCD (Charge Coupled Devices), a CMO (Complementary Metal
Oxide Semiconductor) image sensor, or the like, which is a general
image-pickup element. An image-pickup result can be read at a high
speed, and provision for increasing the number of gradations of the
image-pickup result can be realized.
Advantageous Effects
[0011] According to the present invention, because an amplification
function depends on the source follower circuit, the analog output
can be realized as in the case of a CCD or a CMOS image sensor,
which is a general image-pickup device. The speed of image-pickup
processing can be increased, and the number of gradations of the
image-pickup result can be increased. Thus, by using the
characteristics of the analog output that allows half tones to be
excellently represented, a touch panel function, a scanner
function, or the like can be realized. Furthermore, it can be
considered that the image-pickup devices are applied as dimmer
sensors for a backlight in a liquid-crystal display apparatus.
Moreover, the amplifying thin-film transistor performs the analog
output, thereby realizing the amplification function. Thus, for
example, when TFT-type photosensors are used as the photoelectric
conversion elements, respective constituent elements of the
image-pickup devices can be manufactured using a process the same
as that of typical TFTs. For example, the respective constituent
elements can be disposed in display pixels of a liquid-crystal
display apparatus. In other words, the image-pickup devices are
very suitable for realization of integration with a display
function. In addition, for example, when the image-pickup devices
are embedded in the display pixels of the liquid-crystal apparatus,
the image-pickup devices can be disposed so that a great decrease
in aperture ratio is reduced, and can be easily disposed in a
matrix for the respective display pixels. Thus, for example,
multipoint recognition that was difficult to be realized in touch
panels in the prior art can be realized, and a probability that the
image-pickup devices will serve as key devices of a new user
interface that does not exist in the prior art can be expected.
BRIEF DESCRIPTION OF DRAWINGS
[0012] [FIG. 1] FIG. 1 is a circuit diagram showing an example of a
schematic configuration of a display apparatus according to the
present invention.
[0013] [FIG. 2] FIG. 2 is a circuit diagram showing an example of a
configuration of the main portion in a first embodiment of an
image-pickup device according to the present invention.
[0014] [FIG. 3] FIG. 3 is a timing chart (part 1) showing an
example of drive control in the first embodiment of the present
invention.
[0015] [FIG. 4] FIG. 4 is a timing chart (part 2) showing an
example of drive control in the first embodiment of the present
invention.
[0016] [FIG. 5] FIG. 5 is a timing chart (part 3) showing an
example of drive control in the first embodiment of the present
invention.
[0017] [FIG. 6] FIG. 6 is a timing chart (part 4) showing an
example of drive control in the first embodiment of the present
invention.
[0018] [FIG. 7] FIG. 7 is a circuit diagram showing an example of a
configuration of the main portion in a second embodiment of the
image-pickup device according to the present invention.
[0019] [FIG. 8] FIG. 8 is a timing chart (part 1) showing an
example of drive control in the second embodiment of the present
invention.
[0020] [FIG. ] FIG. 9 is a timing chart (part 2) showing an example
of drive control in the second embodiment of the present
invention.
[0021] [FIG. 10] FIG. 10 is a timing chart (part 3) showing an
example of drive control in the second embodiment of the present
invention.
BEST MODES FOR CARRYING OUT THE INVENTION
[0022] An image-pickup device and a display apparatus according to
the present invention will be described below with reference to the
drawings.
First Embodiment
[0023] First, a first embodiment of the present invention is
described. FIG. 1 is a circuit diagram showing an example of a
schematic configuration of the display apparatus according to the
present invention. FIG. 2 is a circuit diagram showing the first
embodiment of the image-pickup device that is the main portion of
the display apparatus.
[0024] First, the entire display apparatus is described. The
display apparatus that is described in the embodiment is a display
apparatus in which a display function and an image-pickup function
are integrated. In a broad classification, as shown in FIG. 1, the
display apparatus is configured by including an
image-display-region section 1, a backlight or a frontlight
(however, not illustrated) that serves as a light source, and a
driver circuit section (however, not illustrated) for performing
drive control for the image-display-region section 1.
[0025] The image-display-region section 1 is configured of a
plurality of pixel units 2 that are disposed in a matrix.
Additionally, each of the pixel units 2 is configured of a display
element portion 3 and an image-pickup element portion 4. In
addition, various types of signal lines are provided for each row
and each column of the respective pixel units 2, which are disposed
in a matrix. Furthermore, current sources are provided at ends of
the various types of signal lines.
[0026] The display element portion 3 is a display element portion
for providing a function of a so-called p-Si liquid crystal.
Specifically, the display element portion 3 includes a
liquid-crystal display element that is formed on a polycrystalline
silicon (p-Si) substrate. The liquid-crystal display element
selectively transmits light from the backlight or the frontlight,
thereby performing image display. In other words, the display
element portion 3 functions as an image display element in the
present invention in combination with the light source (the
backlight or the frontlight). In addition, although the description
of the details of the p-Si liquid crystal is omitted herein because
the details thereof are commonly known, characteristics can be
obtained, in which the reaction velocity of the liquid crystal is
increased because the p-Si easily conducts electricity compared
with a non-crystalline silicon (a-Si), and also in which brightness
can be increased by increasing an aperture area because the size of
transistors for controlling the liquid crystal can be reduced.
[0027] The image-pickup element portion 4 functions as the
image-pickup device according to the present invention. As shown in
FIG. 2, the image-pickup element portion 4 includes a sensor TFT 5,
a capacitor 6, a reset TFT 7, an amplifying TFT 8, and a reading
TFT 9, which are formed on the p-Si substrate.
[0028] The sensor TFT 5 functions as a photoelectric conversion
element that converts light into electric charge, in which a
leakage current changes in accordance with the amount of received
light. Thus, the source electrode of the sensor TFT 5 is connected
to a power-source line VDD, and the gate electrode thereof is
connected to a bias wire Bias. An applied voltage that causes the
sensitivity and S/N of the sensor to be optimized is applied from
the bias wire Bias to the gate electrode. In addition, the sensor
TFT 5 may be configured using any other element (other than the
TFT) that functions as a photoelectric conversion element, such as
a PN-type diode or a PIN-type diode.
[0029] The capacitor 6 is a passive element that stores and
releases electric charge (electric energy) using a capacitance, and
functions as a storage capacitor that stores electric charge which
the sensor TFT 5 has obtained by conversion. Thus, one end of the
capacitor 6 is connected to a ground wire GND, and the other end
thereof is connected to the sensor TFT 5 and the reset TFT 7. The
capacitor 6 is charged by a photocurrent (electric charge) that is
generated in the sensor TFT 5, whereby a voltage is generated in
accordance with the charge amount. A voltage .DELTA.V that is
converted from a photocurrent .DELTA.I depends on a capacitance
C.sub.p of the capacitor 6 and a light storage time .DELTA.T, and
can be represented by the equation
.DELTA.V=I/C.sub.p.times..DELTA.T. Thus, the longer the light
storage time .DELTA.T and the lower the capacitance C.sub.p of the
capacitor 6, the higher efficiency of conversion from the
photocurrent to the voltage. However, when the capacitance C.sub.p
of the capacitor 6 is markedly low, it should be noted that it is
impossible to disregard an influence of a parasitic capacitance of
the sensor TFT 5 or a parasitic capacitance between wires.
[0030] The reset TFT 7 is disposed between the capacitor 6 and the
ground wire GND in order to discharge the stored electric charge in
the capacitor 6. More specifically, the reset TFT 7 is disposed in
such a manner that the source electrode of the reset TFT 7 is
connected to the ground wire GND, the drain electrode thereof is
connected to the sensor TFT 5 and the capacitor 6, and the gate
electrode thereof is connected to a reset signal line RS.
Accordingly, the reset TFT 7 functions as reset means for
discharging the stored electric charge in the capacitor 6 in
accordance with a reset signal of the reset signal line RS.
[0031] The amplifying TFT 8 receives, amplifies, and outputs the
electric charge stored in the capacitor 6. In other words, the
amplifying TFT 8 has a function of amplifying a voltage
corresponding to the charge amount of the capacitor 6. In addition,
the source electrode of the amplifying TFT 8 is connected to the
power-source line VDD, and the gate electrode thereof is connected
to the sensor TFT 5, the capacitor 6, and the reset TFT 7. The
amplifying TFT 8 forms a source follower circuit together with a
current source that is placed at an end of a sensor signal line
S.
[0032] The reading TFT 9 performs selection of the image-pickup
element portion 4 and reading of an image-pickup result of the
image-pickup element portion 4. The reading TFT 9 is connected to
the amplifying TFT 8 in series, and the gate terminal of the
reading TFT 9 is connected to a reading wire RD. Thus, the reading
TFT 9 is configured so as to be able to perform line-sequentially
reading for the image-pickup result that has been amplified by the
amplifying TFT 8.
[0033] The image-pickup element portions 4 having the
above-described configuration using the combination of the sensor
TFTs 5, the capacitors 6, the reset TFTs 7, the amplifying TFTs 8,
and the reading TFTs 9 are formed on the p-Si substrate. Thus, the
image-display-region section 1 is built as an integrated-type
active-pixel sensor array in which the display element portions 3
and the image-pickup element portions 4 are provided for the
respective pixel units 2 on the same substrate. In other words, the
respective constituent elements of the image-pickup element
portions 4 are integrated, and are individually disposed in
correspondence with the display element portions 3 for the
respective pixel units 2. Thus, the resolution of the image-pickup
results can be made equal to that of displayed image items.
However, the image-pickup element portions 4 are not necessarily
individually disposed for the respective pixel units 2. In other
words, it is only necessary that the image-pickup element portions
4 be disposed in correspondence with the display element portions
3. Disposing of the image-pickup element portions 4 at a
predetermined arrangement density in the image-display-region
section 1, and also disposing of a predetermined number of
image-pickup element portions 4 in the vicinity of the
image-display-region section 1 can be realized.
[0034] In each of the image-pickup element portions 4, which are
configured as described above, electric charge in the capacitor 6
is discharged by a reset process of the reset TFT 7 so that the
capacitor 6 is set to be in an initialization state. After that,
the capacitor 6 is charged by a leakage current of the sensor TFT
5, which changes in accordance with the amount of received light.
Impedance conversion is performed by the amplifying TFT 8, which
forms the source follower circuit, for a voltage across the
capacitor 6 corresponding to the amount of electric charge with
which the capacitor 6 has been charged. After a certain period of
time, the reading TFT 9 is turned on, and a sensor output is read
to the reading wire RD. Accordingly, the image-pickup element
portion 4 functions as the image-pickup device according to the
present invention.
[0035] In this case, in the image-pickup element portion 4, the
amplifying TFT 8 forms the source follower circuit. In other words,
the voltage generated across the capacitor 6 is amplified by the
amplifying TFT 8, and an analog voltage is read to the reading wire
RD. Thus, without setting a complicated image-pickup condition, an
increase in the number of gradations of the image-pickup result can
be realized. In addition, when the source follower circuit is used,
an offset error caused mainly by a variation in Vth among
transistors, a variation in current of the current source circuit,
or the like occurs in an output value. However, for example,
differential processing is performed between the output value and
an output value in a case of no irradiation of light at all, an
output value in a case of reset, or the like, whereby the error can
be removed.
[0036] Next, processing operations in a case in which the
image-pickup element portions 4 configured as described above are
driven are described. FIGS. 3 to 6 are timing charts showing
examples of drive control performed for the image-pickup element
portions 4.
[0037] Regarding the image-display-region section 1 including the
image-pickup element portions 4, which are configured as described
above, the driver circuit section, which performs drive control for
the image-display-region section 1, performs drive control for the
image-display-region section 1 and the light source of the
image-display-region section 1 in units of one-field (hereinafter,
"field" is abbreviated as "F") periods as in the case of a general
liquid-crystal driving method. The above-mentioned 1 F period,
which is a processing unit for drive control, is defined to be, for
example, 16.6 ms.
[0038] For example, in the example of drive control shown in FIG.
3, an F period is defined as a reset period, and the next F period
is defined as a reading period. These periods are repeated. In
addition, in the reset period, discharging of electric charge in
the capacitors 6 is performed by the reset TFTs 7, and reading of
stored electric charge in (voltages across) the capacitors 6
immediately after the discharging of electric charge has been
performed is performed. Additionally, in the reading period,
reading of stored electric charge in the capacitors 6 in a state in
which discharging of electric charge is not performed by the reset
TFTs 7 is performed. In this manner, the amounts of electric charge
that have been converted by the sensor TFTs 5 can be determined
from the differences between respective read results.
[0039] More specifically, as shown in FIG. 3, in a 1 F period that
is a reset period, the driver circuit section applies driving
signals RS1 and RD1 to a reset signal line (hereinafter, simply
referred to as a "row reset line") RS1 and a reading wire
(hereinafter, simply referred to as a "row selection line") RD1 of
a first row disposed in the matrix, thereby selecting the row reset
line RS1 and the row selection line RD1 and setting the reset TFTs
7 and the reading TFTs 9 that are connected to the row reset line
RS1 and the row selection line RD1 to be in on-states. When the
reset TFTs 7 are in the on-state, in the capacitors 6, stored
electric charge is discharged, and the potentials between both
electrodes are commonly set to GND. In addition, when the reading
TFTs 9 are in the on-state, outputs (stored electric charge) at a
point in time at which the capacitors 6 are reset are
line-sequentially read to a sensor signal line S1. An object of
reading of the outputs at the point in time at which the capacitors
6 are reset is to cancel offsets of the amplifying TFTs 8, which
form the source follower circuits, and to greatly reduce output
errors caused by variations in characteristics of the TFTs, by
performing the differential processing between the outputs and
outputs obtained after the following image pickup is performed.
After that, the driving circuit section applies a driving signal
PCG to a pre-charge line PCG, thereby setting TFTs connected to the
pre-charge line PCG to be in an on-state and pre-charging the
sensor signal line S1 at a reference potential. After the
above-described processing operation, the driver circuit section
applies driving signals RS2 and RD2 to a row reset line RS2 and a
row selection line RD2 of a second row disposed in the matrix,
thereby selecting the row reset line RS2 and the row selection line
RD2. The driver circuit section further performs a control process
that is similar to that performed for the first row. Then, the
driver circuit section repeats the above-described series of
processes until it selects a row reset line RSm and a row selection
line RDm of an m-th row, which is the last row disposed in the
matrix, and terminates the 1 F period after performance of the
series of processes is finished for the m-th row.
[0040] In contrast, in a 2 F period that is a reading period,
first, the driver circuit section applies the driving signal RD1 to
the row selection line RD1, thereby selecting the row selection
line RD1 and setting the reading TFTs 9 connected to the row
selection line RD1 to be in an on-state. In this case, image-pickup
results obtained in the 1 F period are maintained as voltages in
the capacitors 6. Thus, when the reading TFTs 9 are in the
on-state, the reading TFTs 9 read the voltages that are maintained
in the capacitors 6 to the sensor signal line S1 via the amplifying
TFTs 8, which form the source follower circuits. After the row
selection line RD1 is selected, the TFTs connected to the
pre-charge line PCG are set to be in an on-state, whereby the
sensor signal line S1 is pre-charged at the reference potential.
After the above-described processing operation, the driver circuit
section applies the driving signal RD2 to the row selection line
RD2, thereby selecting the row selection line RD2. The driver
circuit section further performs a control process that is similar
to that performed for the first row. As in the case of the 1 F
period, the driver circuit section repeats the control process
until it selects the row selection line RDm of the m-th row, which
is the last row, and terminates the 2 F period after performance of
the control process is finished for the m-th row.
[0041] As described above, in the example of drive control shown in
FIG. 3, outputs in the case of a reset operation are
line-sequentially read to sensor signal lines in an odd F period,
and, in an even F period, image-pickup results obtained in the odd
F period that is provided prior to the even F period are
line-sequentially read to the sensor signal lines.
[0042] When output signals are read using the source follower
circuits that the amplifying TFTs 8 form, output voltages need to
reach the ultimate achievable potential in the reading period.
Accordingly, if each F period is short, there is a risk that a
sufficient reading period is not ensured. Thus, it can be
considered that, when there is a risk that it is impossible to
perform reading of n rows in the 1 F period, i.e., when a reading
time of 1 F/n is short for reading of one line, image-pickup
results of odd rows/even rows are read in respective F periods at
drive timing such as that in the example of drive control shown in
FIG. 4. In other words, a vertical frequency is not changed, and a
horizontal frequency is decreased, thereby ensuring a necessary
reading time.
[0043] In other words, in the example of drive control shown in
FIG. 4, reading of the image-pickup results of the even rows is
performed in an F period, and reading of the image-pickup results
of the storage capacitors of the odd rows is performed in the next
F period. In addition, here, suppose that the number m of rows is
an even number, and a description is made as follows.
[0044] Specifically, as shown in FIG. 4, in a 1 F period, the
driver circuit section applies the driving signals RS1, RS2, and
RD1 to the row reset lines RS1 and RS2, and the row selection line
RD1, respectively, thereby selecting the row reset lines RS1 and
RS2, and the row selection line RD1 and setting the reset TFTs 7
and the reading TFTs 9 that are connected to the row reset lines
RS1 and RS2, and the row selection line RD1 to be in on-states.
When the reset TFTs 7 are in the on-state, in the capacitors 6,
stored electric charge is discharged, and the potentials between
both electrodes are commonly set to GND. Additionally, when the
reading TFTs 9 are in the on-state, outputs (stored electric
charge) at a point in time at which the capacitors 6 are reset are
line-sequentially read to the sensor signal lines S1 to Sn.
However, in this case, the row selection line RD2 is not selected.
Thus, outputs of the rows connected to the row selection line RD1
are read. After that, the driving circuit section pre-charges the
sensor signal lines S1 to Sn at the reference potential at a time
at which the driving circuit section applies the driving signal PCG
to the pre-charge line PCG. Then, after the pre-charging, the
driver circuit section selects row reset lines RS3 and RS4, and a
row selection line RD3. After the driver circuit section repeats
the above-described processing operation until row reset lines
RSm-1 and RSm, and a row selection line RDm-1 are selected, the
driver circuit section terminates the 1 F period.
[0045] In the next 2 F period, first, the driver circuit section
applies the driving signal RD1 to the row selection line RD1,
thereby selecting the row selection line RD1 and setting the
reading TFTs 9 connected to the row selection line RD1 to be in an
on-state. In this case, image-pickup results obtained in the 1 F
period are maintained as voltages in the capacitors 6. Thus, when
the reading TFTs 9 are in the on-state, the reading TFTs 9 read the
voltages that are maintained in the capacitors 6 to the sensor
signal lines S1 to Sn via the amplifying TFTs 8, which form the
source follower circuits. After the row selection line RD1 is
selected, the TFTs connected to the pre-charge line PCG are set to
be in an on-state, whereby the sensor signal lines S1 to Sn are
pre-charged at the reference potential. After the above-described
processing operation, the driver circuit section applies the
driving signal RD3 to the row selection line RD3, thereby selecting
the row selection line RD3. After the driver circuit section
further repeats a similar control process for the odd rows until it
selects the row selection line RDm-1, the driver circuit section
terminates the 2 F period.
[0046] In the next 3 F period, the driver circuit section selects
the row reset lines RS1 and RS2, and the row selection line RD2,
and sets the reset TFTs 7 and the reading TFTs 9 that are connected
to the row reset lines RS1 and RS2, and the row selection line RD2
to be in on-states. Thus, the capacitors 6 connected to the drains
of the reset TFTs 7 connected to the row reset lines RS1 and RS2
are reset. Furthermore, outputs (stored electric charge) at a point
in time at which the capacitors 6 are reset are line-sequentially
read to the sensor signal lines S1 to Sn by the reading TFTs 9
connected to the row selection line RD2. After that, the driving
circuit section pre-charges the sensor signal lines S1 to Sn at the
reference potential at a time at which the driving circuit section
applies the driving signal PCG to the pre-charge line PCG. As
described above, in the 3 F period, outputs of the even rows in the
case of reset are obtained via the sensor signal lines S1 to Sn,
which is different from the case of the 1 F period. Then, also in
the case of the 3 F period, as in the case of the 1 F period, after
the driver circuit section repeats the above-described processing
operation until the row reset lines RSm-1 and RSm, and the row
selection line RDm are selected, the driver circuit section
terminates the 3 F period.
[0047] In the next 4 F period, first, the driver circuit section
applies the driving signal RD2 to the row selection line RD2,
thereby selecting the row selection line RD2 and setting the
reading TFTs 9 connected to the row selection line RD2 to be in an
on-state. In this case, image-pickup results obtained in the 3 F
period are maintained as voltages in the capacitors 6. Thus, when
the reading TFTs 9 are in the on-state, the reading TFTs 9 read the
voltages that are maintained in the capacitors 6 to the sensor
signal lines S1 to Sn via the amplifying TFTs 8, which form the
source follower circuits. After the row selection line RD2 is
selected, the TFTs connected to the pre-charge line PCG are set to
be in an on-state, whereby the sensor signal lines S1 to Sn are
pre-charged at the reference potential. After the above-described
processing operation, the driver circuit section applies a driving
signal RD4 to a row selection line RD4, thereby selecting the row
selection line RD4. After the driver circuit section further
repeats a similar control process for the even rows until it
selects the row selection line RDm, the driver circuit section
terminates the 4 F period.
[0048] As described above, in the example of drive control shown in
FIG. 4, since the image-pickup results of the odd rows/even rows
are alternately read in the respective F periods, a reading time
for one horizontal line becomes 1 F/(n/2). Thus, the vertical
frequency is not changed, and the horizontal frequency is
decreased, so that the necessary reading time can be sufficiently
ensured. Specifically, for example, a time can be ensured, which is
twice the reading time for one horizontal line in the example of
drive control described with reference to FIG. 3.
[0049] Furthermore, it can be considered that operation control is
performed for the image-pickup element portions 4 at drive timing
such as that in the example of drive control shown in FIG. 5. In
the example of drive control that is illustrated as an example,
both reading of image-pickup results of rows, and resetting of rows
that are each disposed one row prior to the corresponding row are
performed in one F period.
[0050] Specifically, as shown in FIG. 5, the driver circuit section
applies the driving signal RD1 to the row selection line RD1,
thereby setting the reading TFTs 9 connected to the row selection
line RD1 to be in an on-state. The driver circuit section
line-sequentially reads image-pickup results obtained in the
previous F period to the sensor signal lines S1 to Sn. After that,
the driver circuit section pre-charges the sensor signal lines S1
to Sn at the reference potential at a time at which the driving
circuit section applies the driving signal PCG to the pre-charge
line PCG. Then, after the pre-charging, the driver circuit section
selects the row selection line RD2 and the row reset line RS1, and
sets the reset TFTs 7 and the reading TFTs 9 that are connected to
the row selection line RD2 and the row reset line RS1 to be in
on-states. When the reset TFTs 7 connected to the reset line RS1
are in the on-state, in the capacitors 6, stored electric charge is
discharged, and the potentials between both electrodes are commonly
set to GND. In contrast, because the reading TFTs 9 connected to
the row selection line RD2 are set to be in an on-state at the same
time at which this operation is performed, image-pickup results of
the row that is connected to the row selection line RD2 are read to
the sensor signal lines S1 to Sn. After that, the driving circuit
section pre-charges the sensor signal lines S1 to Sn at the
reference potential. After the pre-charging, the driver circuit
section selects the row selection line RD3 and the row reset line
RS2. The driver circuit section repeats the above-described
processing operation until the row selection line RDm and the row
reset line RSm-1 are selected. Then, finally, the driver circuit
section selects only the row reset line RSm, and resets the
capacitors 6 that are disposed in the row connected to the row
reset line RSm. After the driver circuit section pre-charges the
sensor signal lines S1 to Sn, the driver circuit section terminates
a 1 F period.
[0051] As described above, in the example of drive control shown in
FIG. 5, because a row selection line RDk and a row reset line RSk-1
are driven at the same time for any row k (where k=2 to m-1), the
same wire can be used. In other words, since reading of rows and
resetting of rows that are each disposed one row prior to the
corresponding row are performed in the same F period, signals for
the reading and the resetting can be provided as common signals
using the same wires. Thus, if the same wires using common signals
are used, because the number of wires that exist in the
image-display-region section 1 can be reduced, the aperture ratio
of the image-display-region section 1 can be improved.
[0052] Specifically, in the example of drive control shown in FIG.
5, although commonality of driving signals can be realized, it is
impossible to obtain outputs in the case of a reset operation. The
outputs in the case of a reset operation are very useful in that
offsets of output voltages caused by the source follower circuits
are cancelled, and in that output errors due to variations in
characteristics of the TFTs are greatly reduced, as described using
the example of drive control shown in FIG. 3. In other words, in
order to cancel the offsets of output voltages caused by the source
follower circuits, it is necessary that the offsets be removed
using the differences between image-pickup results and image-pickup
results obtained in a dark room, i.e., in a space in which the
amount of light is zero. Thus, it can be considered that operation
control is performed for the image-pickup element portions 4 at
drive timing such as that in the example of drive control shown in
FIG. 6, whereby the outputs in the case of a reset operation can be
obtained.
[0053] Specifically, as shown in FIG. 6, the driver circuit section
applies the driving signal RD1 to the row selection line RD1,
thereby setting the reading TFTs 9 connected to the row selection
line RD1 to be in an on-state. The driver circuit section
line-sequentially reads image-pickup results obtained in the
previous F period to the sensor signal lines S1 to Sn. After that,
the driver circuit section selects the row reset line RS1 in a
period in which the row selection line RD1 is selected. By
selecting the row reset line RS1, outputs in the case of a reset
operation are line-sequentially read to the sensor signal lines S1
to Sn. In other words, by performing the above-described drive
control, the image-pickup results obtained in the previous F period
and the outputs in the case of a reset operation can be obtained in
a reading period for one horizontal line. In this case, when the
differences between the image-pickup results and the outputs in the
case of a reset operation are obtained, the output offsets caused
by the source follower circuits can be removed, for example, by
utilizing a CDS (correlated double sampling) circuit that is
generally used to drive a CCD. After that, the driver circuit
section pre-charges the sensor signal lines S1 to Sn at the
reference potential at a time at which the driving circuit section
applies the driving signal PCG to the pre-charge line PCG. Then,
after the pre-charging, the driver circuit section selects the row
selection line RD2 and sets the reading TFTs 9 connected to the row
selection line RD2 to be in an on-state. The driver circuit section
further repeats a similar control process until the row selection
line RDm is selected.
[0054] As described above, in the example of drive control shown in
FIG. 6, both reading of the image-pickup results and resetting are
performed in the same clock cycle in one F period, and the
differences between the image-pickup results and the outputs in the
case of a reset operation can be obtained. Accordingly, even when
the number of wires that exist in the image-display-region section
1 is reduced in order to improve the aperture ratio of the
image-display-region section 1, the offsets of output voltages
caused by the source follower circuits can be cancelled, and the
output errors due to variations in characteristics of the TFTs can
be greatly reduced.
[0055] According to the image-pickup element portions 4 in the
above-described first embodiment, even in the case of any one of
the examples of driven control shown in FIGS. 3 to 6, the
amplifying TFTs 8 form the source follower circuits. Accordingly,
when electric charge (image-pickup results) stored in the
capacitors 6 are read, analog output can be performed by utilizing
the source follower circuits. Thus, for example, even when the
respective elements 5 to 9 constituting the image-pickup element
portions 4 are formed on the p-Si substrate in order to be easily
integrated with the display function, analog output can be realized
as in the case of CCDs or CMOS image sensors, which are general
image-pickup elements, whereby the speed of image-pickup processing
can be increased and the number of gradations of the image-pickup
results can be increased.
[0056] Additionally, according to the image-pickup element portions
4 in the first embodiment, since the sensor TFTs 5 are used as
photoelectric conversion elements, the sensor TFTs 5 can be
manufactured using a typical TFT manufacturing method, i.e., using
a portion of a general manufacturing process of liquid-crystal
display elements. Furthermore, an exactly similar thing can be also
applied to the reset TFTs 7, which function as reset means. Thus,
according to the image-pickup element portions 4 in the first
embodiment, the respective constituent elements can be manufactured
using a process the same as that of typical TFTs. For example, the
image-pickup element portions 4 have the respective constituent
elements that can be easily disposed in the pixel units 2 of the
liquid-crystal display apparatus. In other words, the image-pickup
element portions 4 are very suitable for realization of integration
with the display function.
[0057] In addition, according to the image-pickup element portions
4 in the embodiment, the respective constituent elements 5 to 9 are
integrated and disposed in correspondence with the respective pixel
units 2, which are disposed in the matrix. Thus, for example, not
only a touch panel function or a scanner function can be realized,
but also multipoint recognition that was difficult to be realized
in touch panels in the prior art can be realized. There is a
probability that the image-pickup element portions 4 will serve as
key devices of a new user interface that does not exist in the
prior art. Furthermore, it can be considered that the image-pickup
element portions 4 are utilized as dimmer sensors for the backlight
in the display element portions 3 by using the characteristics of
the analog output.
Second Embodiment
[0058] Next, a second embodiment of the present invention will be
described. However, herein, only the difference between the second
embodiment and the above-described first embodiment is
described.
[0059] In the first embodiment, the reset TFT 7 is provided as
reset means. Accordingly, when the image-pickup element portion 4
is disposed in each of the respective pixel units 2, which are
disposed in the matrix, a decrease in the aperture ratio of the
display element portion 3 only by a portion corresponding to the
provided reset TFT 7 may occur. In contrast, although the gate
voltage of the sensor TFT 5 is set to be equal to or lower than a
threshold when the sensor TFT 5 is used as a photoelectric
conversion element, it is known that, if the setting of the gate
voltage is appropriately changed, the sensor TFT 5 can operate as a
normal transistor. Thus, in an image-pickup element portion 4 that
is to be described as an example in the embodiment, the gate
voltage of the sensor TFT 5 is changed, thereby properly using a
photoelectric conversion function and a reset function of the
sensor TFT 5. Accordingly, integration of the reset function for
the capacitor 6 is realized without the reset TFT 7.
[0060] FIG. 7 is a circuit diagram showing an example of a
configuration of the main portion of an image-pickup device
according to the second embodiment of the present invention.
Although the image-pickup element portion 4, which is illustrated
as an example, includes the sensor TFT 5, the capacitor 6, the
amplifying TFT 8, and the reading TFT 9, which are formed on a p-Si
substrate, as in the case of the first embodiment, the reset TFT 7
is not formed, which is different from the case of the first
embodiment.
[0061] The bias wire Bias is connected to the gate electrode of the
sensor TFT 5, and the power-source line VDD is connected to the
drain electrode of the sensor TFT 5. In addition, when a voltage
value that is applied via the bias wire Bias is lower than a
predetermined threshold, the sensor TFT 5 functions as a
photoelectric conversion element. In other words, when the
predetermined threshold is set so as to cause the sensitivity and
S/N of the sensor to be optimized and a voltage lower than the
threshold voltage is applied to the bias wire Bias, the sensor TFT
5 functions as a photoelectric conversion element. In contrast,
when the applied voltage value is equal to or higher than the
threshold, the sensor TFT 5 functions as a switching TFT, and
discharges electric charge in the capacitor 6 so that the capacitor
6 is reset to enter an initialization state. In other words, when
the voltage that is equal to or higher than the threshold is
applied to the bias wire Bias and a voltage of the power-source
line VDD is set to have the ground (GND) potential, the sensor TFT
5 functions as a reset TFT. As described above, as in the case of
the above-mentioned configuration in the embodiment, even in a case
in which the image-pickup element portion 4 does not include the
reset TFT 7, when the voltages that are applied to the bias wire
Bias and the power-source line VDD are changed in accordance with a
lapse of time, the sensor TFT 5 functions as a photoelectric
conversion element or a reset TFT.
[0062] In other words, in the image-pickup element portion 4
according to the second embodiment, the reset function that the
sensor TFT 5 has, and a function of switching the gate voltage that
is to be applied to the sensor TFT 5 realize a function of the
reset means for discharging stored electric charge in the capacitor
6. In other words, for the sensor TFT 5 that functions as a
photoelectric conversion element when the gate voltage is lower
than the threshold, the image-pickup element portion 4 is
configured so as to discharge electric charge in the capacitor 6 by
switching the gate voltage of the sensor TFT 5 so that the gate
voltage is set to be equal to or higher than the threshold.
[0063] Next, processing operations in a case in which the
image-pickup element portions 4 configured as described above are
driven are described. FIGS. 8 to 10 are timing charts showing
examples of drive control performed for the image-pickup element
portions 4.
[0064] For example, in the example of drive control shown in FIG.
8, an F period is defined as a reset period, and the next F period
is defined as a reading period. These periods are repeated. In
addition, in the reset period, discharging of electric charge in
the capacitors 6 is performed, and reading of stored electric
charge in (voltages across) the capacitors 6 immediately after the
discharging of electric charge has been performed is performed.
Additionally, in the reading period, reading of stored electric
charge in the capacitors 6 in a state in which discharging of
electric charge is not performed is performed. In this manner, the
amounts of electric charge that are converted by the sensor TFTs 5
can be determined from the differences between respective read
results.
[0065] More specifically, as shown in FIG. 8, in a 1 F period, the
driver circuit section applies a driving signal Bias1 to a bias
line Bias1 of the first row disposed in the matrix, thereby setting
the sensor TFTs 5 connected to the bias line Bias1 to be in an
on-state. Then, the driver circuit section applies a driving signal
VDD1 to a power-source line VDD1 when the sensor TFTs 5 are in the
on-state. Accordingly, electric charge that exists in the
capacitors 6 is discharged via the sensor TFTs 5 connected to the
bias line Bias1, and the potentials between both electrodes of the
capacitors 6 are commonly set to GND. After that, the driver
circuit section sets a voltage applied to the bias line Bias1 to
have a low level, thereby setting the sensor TFTs 5 connected to
the bias line Bias1 to be in an off-state. Here, the voltage
applied to the bias line Bias1 has a voltage value that is lower
than the threshold of the sensor TFTs 5. Then, the driver circuit
section sets a voltage applied to the power-source line VDD1 to
have a high level when the sensor TFTs 5 are in the off-state.
Accordingly, the sensor TFTs 5 connected to the bias line Bias1
function as photoelectric conversion elements, and the capacitors 6
is charged with electric charge in accordance with light with which
the sensor TFTs 5 are irradiated. After that, the driver circuit
section selects a bias line Bias2 and a power-source line VDD2, and
further performs a control process that is similar to that
performed for the first row. Then, the driver circuit section
repeats the above-described series of processes until it selects a
bias line Biasm and a power-source line VDDm of the m-th row, which
is the last row disposed in the matrix, and terminates the IF
period after performance of the series of processes is finished for
the m-th row. In the IF period, the sensor signal lines S1 to Sn
are always pre-charged at the reference potential using the driving
signal PCG that is applied to the pre-charge line PCG.
[0066] In contrast, in a 2 F period that is a reading period,
first, the driver circuit section applies the driving signal RD1 to
the row selection line RD1, thereby selecting the row selection
line RD1 and setting the reading TFTs 9 connected to the row
selection line RD1 to be in an on-state. In this case, image-pickup
results obtained in the 1 F period are maintained as voltages in
the capacitors 6. Thus, when the reading TFTs 9 are in the
on-state, the reading TFTs 9 read the voltages that are maintained
in the capacitors 6 to the sensor signal line S1 via the amplifying
TFTs 8, which form the source follower circuits. After the row
selection line RD1 is selected, the TFTs connected to the
pre-charge line PCG are set to be in an on-state, whereby the
sensor signal line S1 is pre-charged at the reference potential.
After the above-described processing operation, the driver circuit
section applies the driving signal RD2 to the row selection line
RD2, thereby selecting the row selection line RD2. The driver
circuit section further performs a control process that is similar
to that performed for the first row. As in the case of the 1 F
period, the driver circuit section repeats the control process
until it selects the row selection line RDm of the m-th row, which
is the last row, and terminates the 2 F period after performance of
the control process is finished for the m-th row.
[0067] As described above, in the example of drive control shown in
FIG. 8, all of the sensor signal lines are maintained at the
reference potential in an odd F period, and image-pickup results
obtained in the 1 F period are line-sequentially read to the sensor
signal lines in an even F period.
[0068] Additionally, for example, in the example of drive control
shown in FIG. 9, also when output signals are read using the source
follower circuits, in order to ensure a necessary reading time in
such a manner that a vertical frequency is not changed, and that a
horizontal frequency is decreased, reading of image-pickup results
of the even rows is performed in an F period, and reading of
image-pickup results of the storage capacitors of the odd rows is
performed in the next F period.
[0069] More specifically, as shown in FIG. 9, in a 1 F period, the
driver circuit section applies the driving signals Bias1, Bias2,
VDD1, and VDD2 to the bias lines Bias1 and Bias2, and the
power-source lines VDD1 and VDD2, respectively, thereby setting the
sensor TFTs 5 connected to the bias lines Bias1 and Bias2, and the
power-source lines VDD1 and VDD2 to be in an on-state. The
power-source lines VDD1 and VDD2 have a low level when the sensor
TFTs 5 are in the on-state. Accordingly, electric charge that
exists in the capacitors 6 is discharged via the sensor TFTs 5, and
the potentials between both electrodes of the capacitors 6 are
commonly set to GND. Furthermore, the reading TFTs 9 are set to be
in an on-state, whereby outputs (stored electric charge) at a point
in time at which the capacitors 6 are reset are line-sequentially
read to the sensor signal lines S1 to Sn. However, in this case,
the row selection line RD2 is not selected. Thus, outputs of the
rows connected to the row selection line RD1 are read. After that,
the driving circuit section pre-charges the sensor signal lines S1
to Sn at the reference potential at a time at which the driving
circuit section applies the driving signal PCG to the pre-charge
line PCG. Then, after the pre-charging, the driver circuit section
selects power-supply line VDD3 and VDD4, and the row selection line
RD3. After the driver circuit section repeats the above-described
processing operation until power-source line VDDm-1 and VDDm, and
the row selection line RDm-1 are selected, the driver circuit
section terminates the 1 F period.
[0070] In the next 2 F period, first, the driver circuit section
applies the driving signal RD1 to the row selection line RD1,
thereby selecting the row selection line RD1 and setting the
reading TFTs 9 connected to the row selection line RD1 to be in an
on-state. In this case, image-pickup results obtained in the 1 F
period are maintained as voltages in the capacitors 6. Thus, when
the reading TFTs 9 are in the on-state, the reading TFTs 9 read the
voltages that are maintained in the capacitors 6 to the sensor
signal lines S1 to Sn via the amplifying TFTs 8, which form the
source follower circuits. After the row selection line RD1 is
selected, the TFTs connected to the pre-charge line PCG are set to
be in an on-state, whereby the sensor signal lines S1 to Sn are
pre-charged at the reference potential. After the above-described
processing operation, the driver circuit section applies the
driving signal RD3 to the row selection line RD3, thereby selecting
the row selection line RD3. After the driver circuit section
further repeats a similar control process for the odd rows until it
selects the row selection line RDm-1, the driver circuit section
terminates the 2 F period.
[0071] In the next 3 F period, the driver circuit section applies
the driving signals Bias1, Bias2, VDD1, and VDD2 to the bias lines
Bias1 and Bias2, and the power-source lines VDD1 and VDD2,
respectively, thereby setting the sensor TFTs 5 connected to the
bias lines Bias1 and Bias2, and the power-source lines VDD1 and
VDD2 to be in an on-state. Thus, the capacitors 6 are reset.
Furthermore, outputs (stored electric charge) at a point in time at
which the capacitors 6 are reset are line-sequentially read to the
sensor signal lines S1 to Sn by the reading TFTs 9 connected to the
row selection line RD2. After that, the driving circuit section
pre-charges the sensor signal lines S1 to Sn at the reference
potential at a time at which the driving circuit section applies
the driving signal PCG to the pre-charge line PCG. As described
above, in the 3 F period, outputs of the even rows in the case of
reset are obtained via the sensor signal lines S1 to Sn, which is
different from the case of the 1 F period. Then, also in the case
of the 3 F period, as in the case of the 1 F period, after the
driver circuit section repeats the above-described processing
operation until the power-source line VDDm-1 and VDDm, and the row
selection line RDm are selected, the driver circuit section
terminates the 3 F period.
[0072] In the next 4 F period, first, the driver circuit section
applies the driving signal RD2 to the row selection line RD2,
thereby selecting the row selection line RD2 and setting the
reading TFTs 9 connected to the row selection line RD2 to be in an
on-state. In this case, image-pickup results obtained in the 3 F
period are maintained as voltages in the capacitors 6. Thus, when
the reading TFTs 9 are in the on-state, the reading TFTs 9 read the
voltages that are maintained in the capacitors 6 to the sensor
signal lines S1 to Sn via the amplifying TFTs 8, which form the
source follower circuits. After the row selection line RD2 is
selected, the TFTs connected to the pre-charge line PCG are set to
be in an on-state, whereby the sensor signal lines S1 to Sn are
pre-charged at the reference potential. After the above-described
processing operation, the driver circuit section applies the
driving signal RD4 to the row selection line RD4, thereby selecting
the row selection line RD4. After the driver circuit section
further repeats a similar control process for the even rows until
it selects the row selection line RDm, and terminates the 4 F
period.
[0073] As described above, in the example of drive control shown in
FIG. 9, since the image-pickup results of the odd rows/even rows
are alternately read in the respective F periods, a reading time
for one horizontal line becomes 1 F/(n/2). Thus, the vertical
frequency is not changed, and the horizontal frequency is
decreased, so that the necessary reading time can be sufficiently
ensured. Specifically, for example, a time can be ensured, which is
twice the reading time for one horizontal line in the example of
drive control described with reference to FIG. 3.
[0074] Furthermore, for example, in the example of drive control
shown in FIG. 10, both reading of image-pickup results of rows, and
resetting of rows that are each disposed one row prior to the
corresponding row are performed in one F period.
[0075] Specifically, as shown in FIG. 10, the driver circuit
section applies the driving signal RD1 to the row selection line
RD1, thereby setting the reading TFTs 9 connected to the row
selection line RD1 to be in an on-state. The driver circuit section
line-sequentially reads image-pickup results obtained in the
previous F period to the sensor signal lines S1 to Sn. After that,
the driver circuit section pre-charges the sensor signal lines S1
to Sn at the reference potential at a time at which the driving
circuit section applies the driving signal PCG to the pre-charge
line PCG. Then, after the pre-charging, the driver circuit section
applies the driving signals RD2, Bias1, and VDD1. Accordingly,
because the power-source lines VDD1 and VDD2 have a low level when
the sensor TFTs 5 connected to the power-source line VDD1 are in an
on-state, electric charge that exists in the capacitors 6 is
discharged via the sensor TFTs 5, and the potentials between both
electrodes of the capacitors 6 are commonly set to GND. In
contrast, because the reading TFTs 9 connected to the row selection
line RD2 are set in an on-state at the same time at which this
operation is performed, image-pickup results of the row that is
connected to the row selection line RD2 are read to the sensor
signal lines S1 to Sn. Then, the driving circuit section
pre-charges the sensor signal lines S1 to Sn at the reference
potential. After the pre-charging, the driver circuit section
applies the driving signals RD3, Bias2, and VDD2. The driver
circuit section repeats the above-described processing operation
until the row selection line RDm, and the power-source line VDDm-1
are selected. Then, finally, the driver circuit section selects
only the power-supply line VDDm, and resets the capacitors 6 that
are disposed in the row connected to the power-source line VDDm.
After the driver circuit section pre-charges the sensor signal
lines S1 to Sn, the driver circuit section terminates a 1 F
period.
[0076] As described above, in the example of drive control shown in
FIG. 10, because a row selection line RDk and a power-supply line
VDDk-1 are driven at the same time for any row k (where k=2 to
m-1), the same wire can be used. In other words, since reading of
rows and resetting of rows that are each disposed one row prior to
the corresponding row are performed in the same F period, signals
for the reading and the resetting can be provided as common signals
using the same wires. Thus, if the same wires using common signals
are used, because the number of wires that exist in the
image-display-region section 1 can be reduced, the aperture ratio
of the image-display-region section 1 can be improved.
[0077] In addition, although the description is omitted here, also
in the second embodiment, for example, as in the example of drive
control shown in FIG. 6 in the first embodiment, both reading of
the image-pickup results and resetting may be performed in the same
clock cycle in one F period, and the differences between the
image-pickup results and the outputs in the case of a reset
operation may be obtained.
[0078] According to the image-pickup element portions 4 in
above-described second embodiment, even in the case of any one of
the examples of driven control shown in FIGS. 8 to 10, the
amplifying TFTs 8 form the source follower circuits as in the case
of the first embodiment. Accordingly, when electric charge
(image-pickup results) stored in the capacitors 6 are read, analog
output can be performed by utilizing the source follower circuits.
Thus, for example, even when the respective elements 5 to 9
constituting the image-pickup element portions 4 are formed on the
p-Si substrate in order to be easily integrated with the display
function, analog output can be realized as in the case of CCDs or
CMOS image sensors, which are general image-pickup elements,
whereby the speed of image-pickup processing can be increased and
the number of gradations of the image-pickup results can be
increased.
[0079] Furthermore, according to the image-pickup element portion 4
in the second embodiment, the gate voltage of the sensor TFT 5 is
changed, thereby properly using the photoelectric conversion
function and the rest function of the sensor TFT 5. Accordingly,
because integration of the reset function for the capacitor 6 is
realized without the reset TFT 7, the circuit scale of the
image-pickup element portion 4 can be reduced, and, even when
integration with the display function is realized, the aperture
ratio of the display element portion 3 is not decreased.
[0080] Additionally, the above-described first and second
embodiments are described as preferable embodiments according to
the present invention. The present invention is not limited to the
contents of the embodiments. Modifications may be appropriately
made without departing from the gist of the present invention.
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